Our laboratory has been actively studying the pathogenesis of alcoholic liver disease, focusing on how acetaldehyde dehydrogenase 2 (ALDH2)and miRNA-223 on fatty liver disease and its associated liver cancer. First, we have demonstrated that ALDH2 deficiency promotes alcohol-associated liver cancer by activating oncogenic pathways via oxidized DNA enriched extracellular vesicles. Abstracts: BACKGROUND & AIMS: Excessive alcohol drinking is one of the major causes of hepatocellular carcinoma (HCC). Approximately 30-40% Asian population are deficient for aldehyde dehydrogenase 2 (ALDH2), a key enzyme to detoxify the ethanol metabolite acetaldehyde. However, how ALDH2 deficiency affects alcohol-related HCC remains obscure. METHODS: ALDH2 polymorphism in 646 patients with viral hepatitis B (HBV) infection with or without alcohol drinking was studied. A new model of HCC induced by chronic carbon tetrachloride (CCl4) and alcohol administration was developed and studied in three lines of Aldh2-deficient mice: including Aldh2 global knockout (KO) mice, Aldh2*1/*2 knock-in mutant mice, and liver-specific Aldh2 KO mice. RESULTS: We demonstrated that ALDH2 deficiency was not associated with liver disease progression but was associated with an increased risk of HCC development in cirrhotic HBV patients with excessive alcohol consumption. The mechanisms underlying HCC development associated with cirrhosis and alcohol consumption were studied in Aldh2-deficient mice. We found that all three lines of Aldh2-deficient mice were more susceptible to CCl4 plus alcohol-associated liver fibrosis and HCC development. Furthermore, our results from in vivo and in vitro mechanistic studies revealed that after CCl4 plus ethanol exposure, Aldh2-deficient hepatocytes produced a large amount of harmful oxidized mtDNA via extracellular vesicles (EVs), which were then transferred into neighboring HCC cells and together with acetaldehyde activated multiple oncogenic pathways (JNK, STAT3, BCL-2, and TAZ), thereby promoting HCC. CONCLUSIONS: ALDH2 deficiency is associated with an increased risk of alcohol related-HCC development from fibrosis in patients and in mice. Mechanistic studies reveal a novel mechanism that Aldh2-deficient hepatocytes promote alcohol-associated HCC by transferring harmful oxidized mtDNA-enriched EVs into HCC and subsequently activating multiple oncogenic pathways in HCC. Second, we have demonstrated that microRNA-223 ameliorates nonalcoholic steatohepatitis and cancer by targeting multiple inflammatory and oncogenic genes in hepatocytes. Abstract: Nonalcoholic fatty liver disease (NAFLD) represents a spectrum of diseases ranging from simple steatosis to more severe forms of liver injury including nonalcoholic steatohepatitis (NASH), fibrosis, and hepatocellular carcinoma (HCC). In humans, only 20%-40% of patients with fatty liver progress to NASH, and mice fed a high-fat diet (HFD) develop fatty liver but are resistant to NASH development. To understand how simple steatosis progresses to NASH, we examined hepatic expression of anti-inflammatory microRNA-223 (miR-223) and found that this miRNA was highly elevated in hepatocytes in HFD-fed mice and in human NASH samples. Genetic deletion of miR-223 induced a full spectrum of NAFLD in long-term HFD-fed mice including steatosis, inflammation, fibrosis, and HCC. Furthermore, microarray analyses revealed that, compared to wild-type mice, HFD-fed miR-223 knockout (miR-223KO) mice had greater hepatic expression of many inflammatory genes and cancer-related genes, including (C-X-C motif) chemokine 10 (Cxcl10) and transcriptional coactivator with PDZ-binding motif (Taz), two well-known factors that promote NASH development. In vitro experiments demonstrated that Cxcl10 and Taz are two downstream targets of miR-223 and that overexpression of miR-223 reduced their expression in cultured hepatocytes. Hepatic levels of miR-223, CXCL10, and TAZ mRNA were elevated in human NASH samples, which positively correlated with hepatic levels of several miR-223 targeted genes as well as several proinflammatory, cancer-related, and fibrogenic genes. Conclusion: HFD-fed miR-223KO mice develop a full spectrum of NAFLD, representing a clinically relevant mouse NAFLD model; miR-223 plays a key role in controlling steatosis-to-NASH progression by inhibiting hepatic Cxcl10 and Taz expression and may be a therapeutic target for the treatment of NASH.